IEC 61937-8 pdf download – Digital Audio – Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 – Part 8: Non-linear PCM bitstreams according to the Windows Media Audio (WMA) Professional format

IEC 61937-8 pdf download – Digital Audio – Interface for non-linear PCM encoded audio bitstreams applying IEC 60958 – Part 8: Non-linear PCM bitstreams according to the Windows Media Audio (WMA) Professional format
5.3 Audio data-bursts
5.3.1 The data-burst for WMA Professional
Type I WMA Professional Type I is primarily intended for use at sample rates above 48 kHz (for example, 88,2 kHz or 96 kHz). The IEC 60958 link should be operated at the sample rate of the decoded audio. The WMA Professional bitstream consists of a sequence of WMA Professional frames. The data-type of a WMA Professional Type I data-burst is 1 2 h and the subtype is 0 h. A WMA Professional Type I frame represents 4 096 samples of each encoded audio channel (left, centre, etc.) transmitted in two sequential data-bursts.
The data-burst is headed with a burst- preamble, followed by the burst-payload. The burst-payload of each pair of data-bursts of WMA Professional Type I data shall contain one complete WMA Professional frame. The length of the WMA Professional data-burst will depend on the encoded bit rate (which determines the WMA Professional frame length).
The data-bursts containing WMA Professional Type I frames shall occur at a regular rate, with the reference point of each WMA Professional frame (bit 0 of Pa of the first of the pair of data- bursts) beginning (except in the case of a gap) 4 096 sampling periods of the audio after the reference point of the preceding WMA Professional frame (of the same bit-stream-number).
5.3.2 Latency of WMA Professional Type I decoding The latency of an audio decoder to decode a Windows Media Audio Professional data-burst is defined as two Windows Media Audio Professional frames, plus a decoding delay of two-thirds of a Windows Media Audio Professional frame. This corresponds to a latency of 1 23,84 ms at 88,2 kHz and 1 1 3,77 ms at 96 kHz sampling frequency, where the maximum frame size is 4 096 samples per frame.
It is recommended that Pause data-bursts are used to fill stream gaps in the WMA Professional bit-stream as described in IEC 61 937-1 , and that Pause data-bursts be transmitted with a repetition period of three sampling periods of the audio, except when other repetition periods are necessary to fill the precise stream gap length (which may not be a multiple of three sampling periods of the audio), or to meet the requirement on burst spacing (see IEC 61 937-1 , 6.3.3). When a stream gap in a WMA Professional Type I stream is filled by a sequence of Pause data-bursts, the Pa of the first Pause data-burst shall be located 2 048 sampling periods following the Pa of the previous WMA Professional frame. It is recommended that the sequence(s) of Pause data-bursts which fill the stream gap should continue from this point up to (as close as possible considering the three IEC 60958 frame length of the Pause data- burst) the Pa of the first WMA Professional data-burst which follows the stream gap. The gap- length parameter contained in the Pause data-burst is intended to be interpreted by the WMA Professional decoder as an indication of the number of decoded PCM samples which are missing (due to the resulting audio gap).
5.3.3 The data-burst for WMA Professional Type II The WMA Professional bitstream consists of a sequence of WMA Professional frames. The data-type of a WMA Professional Type II data-burst is 1 2 h and the subtype is 1 h. A WMA Professional Type II frame represents 2 048 samples of each encoded audio channel (left, centre, etc.). The data-burst is headed with a burst-preamble, followed by the burst-payload. The burst-payload of each data-burst of WMA Professional Type II data shall contain one complete WMA Professional frame. The length of the WMA Professional data-burst will depend on the encoded bit rate (which determines the WMA Professional frame length).